Naslov
Quantitative Analysis of Chemical Elements Sorbed in the Lamellar Liquid Crystalline Phases Determined by Scanning Electron Microscopy

Autori
Tudja, Marijan ; Galešić, Mirna ; Težak, Đurđica

Izvornik
Journal of computer-assisted microscopy (1040-7286) 9 (1997); 65-66

Vrsta, podvrsta i kategorija rada
Radovi u časopisima, članak, znanstveni

Ključne riječi
Amphiphiles; Lamellar; Cadmium Dodecylbenzenesulphonate

Sažetak
The structures built by amphiphilic molecules in the presence of water are different from classical molecular crystals. The micelles of various shapes, liquid crystals, sponge phases, bicontinuous phases, vesicles, microemulsions, and crystalline solids were found in the binary surfactant / water systems, and in more-component systems [1-3]. Cadmium dodecylbenzenesulphonate precipitates from water solutions both, in the crystal and liquid crystal phase. The solubility product of the crystal form, kso=(3.6ą0.6)x10-12, was determined using light scattering method ; the stoichiometric relation [Cd++] : [DBS-] = 1 : 2 was fully satisfied. This concentration relation was different in the case of the liquid crystal formation, [Cd++] : [DBS-] = 7 : 1, i.e., it is shifted towards higher cadmium concentration due to the sorption of cadmium into the viscous liquid crystal matrix. A good agreement of the results achieved by the complexometric analysis, atomic absorption, X-ray diffraction, as well as, thermogravimetric analysis, was found. These methods showed that the cadmium partly was included into the lamellar bilayers, and it was partly crystallized within the liquid crystal matrix ; in addition, at high temperatures cadmium was transformed to its elementary state. It can be assumed that some amount of cadmium has been adsorbed at negatively charged surface of the surfactant micelles. The results of these quantitative analyses have been confirmed by the determination of the structures using a new Jeol JSM-5800 scanning electron microscope (SEM). In this investigation, required concentrations for the formation of liquid crystals from the solution were: [Cd(NO3)2] = 2.5x10-3 mol dm-3, [HDBS] = 1.0x10-3 mol dm-3. Identification of liquid crystalline phases was performed on a Leitz Wetzlar light microscope (LM) with polarizing equipment. Samples were prepared by putting the colloidal suspension from a test tube in between object and cover glass. The formation of the lamellar phases as followed by LM was exhibited by optical birefringence. The results of the analysis of the characteristic X-ray energy detectors for the chemical elements that are present in the liquid crystalline samples were performed by SEM ; they are represented for cadmium in Figures 1 and 2. The high density of the points in Figure 1 represents the dense distribution of this element at the surface of the liquid crystalline aggregated particle. In addition, the linear analysis of the characteristic X-ray emission pattern for this particular element is represented in Figure 2. The high content of cadmium at the surface of the particle is shown. Figure 1 SEM mapping picture representing the distribution of cadmium at the liquid crystalline surface. Magnification: 16000x. Figure 2 SEM linear analysis of the surface of the liquid crystalline aggregate of cadmium dodecylbenzenesulphonate. References (1) H. Hoffmann, C. Thunig, U. Munkert, H. W. Meyer and W. Richter, Langmuir, 8 (1992) 2629. (2) J. Charvolin, Progr. Colloid and Polymer Sci. 81 (1990) 6. (3) K. A. Dawson, Pure & Appl. Chem. 64 (1992) 1589.

Izvorni jezik
Engleski

Znanstvena područja
Kemija, Biologija

POVEZANOST RADA